The businessman filed the lawsuit at London's High Court on July 20 against several defendants, including Russian state nuclear energy company Rosatom, oil pipeline operator Transneft, private equity firm TPG and UAE-based port operator DP World.

Magomedov, 55, claims his 2018 arrest on embezzlement charges prompted a Russian state-supported expropriation scheme, largely for the benefit of Rosatom and Transneft, according to court filings.

He alleges the Russian state wanted to bring transportation group Fesco - which operates ports, including a key port in Vladivostok - under Rosatom's control.

He is suing TPG, DP World, Rosatom and others over the alleged conspiracy to acquire his interest in Fesco, which he values at $8.8 billion.

A TPG spokesperson said Magomedov's claims are "entirely without merit".

"We intend to defend ourselves vigorously against such allegations," they added.

DP World, Transneft and Rosatom did not immediately respond to requests for comment.

Magomedov also alleges Transneft conspired to take his and his brother Magomed Magomedov's interest in Novorossiysk Commercial Sea Port (NCSP).

The Magomedovs acquired their interest in NCSP through a joint venture with Transneft and were negotiating to sell their shares for around $1.3 billion, according to court filings.

However, Magomedov alleges Transneft representatives told him after his arrest that Transneft president Nikolay Tokarev would speak to Russian President Vladimir Putin and procure his release if he sold the shares for $750 million.

Magomedov was once one of Russia's richest men, with assets in construction and logistics through his sprawling Summa Group. His net worth in the year before his arrest was estimated by Forbes magazine at $1.4 billion.

But he was convicted last year on organised crime and embezzlement charges, following one of the highest-profile prosecutions of a Russian tycoon in years.

Magomedov was sentenced to 19 years in a high-security prison. He says the charges are unfounded and is appealing against his conviction.

(Reporting by Sam Tobin; Additional reporting by Reuters in Moscow; Editing by Peter Graff)